Alluvial architecture of mid‐channel fluvial–tidal barforms: The mesotidal Lower Columbia River, Oregon/Washington, USA
Bibliographic record
Abstract
Abstract Barforms of mesotidal to macrotidal fluvial–tidal transitions, regardless of fluvial‐discharge, are currently thought to display a sedimentary architecture dominated by tidal signatures. Due to the scarcity of observations from modern mesotidal fluvial–tidal transitions, especially those of multi‐channelled large‐rivers (mean annual discharge ≥7000 m3 s−1 and peak discharges ≥15 000 m3 s−1) with mid‐channel bars, this concept remains unproven. The present study analyses data produced by a combination of high‐resolution ground penetrating radar and coupled shallow vibracores (<5 m depth), collected from modern fluvial–tidal mid‐channel bars of the mesotidal multi‐channelled Lower Columbia River, Washington/Oregon, USA, which can experience peak discharges ≥18 000 m3 s−1. These data were used alongside time‐sequenced aerial imagery to characterize the spatio‐temporal sedimentological evolution of these barforms in singular flows or combined flows consisting of river, tidal and/or wind‐wave oscillatory, current components operating in unique fluvial–tidal transition regimes. Results indicate that ca 75% of the Lower Columbia River fluvial–tidal transition produces braid‐bars with basal to bar‐top sedimentological architectures that are indistinguishable from fluvial‐only braid‐bars recorded in the literature. Barform stratal characteristics within the fluvial–tidal transitions of mesotidal large‐rivers are therefore more likely to be dominated by downstream‐oriented currents. Furthermore, a new style of low‐angle (<5°) inclined heterolithic stratification found in bar‐top accretion‐sets within upper‐mixed tidal–fluvial regime braid‐bars is observed. This common stratification is created by combined‐flows characterized by intrabasinal wind‐wave oscillatory‐currents and bidirectional tidal‐currents. This inclined heterolithic stratification marks the initial downstream fluvial–tidal crossover point from Lower Columbia River up‐dip fully‐fluvial braid‐bar architectures, to those possessing bar‐top facies produced by the hydraulic‐sedimentation response of combined intrabasinal wind‐wave and tidal influence. When preserved, this form of mid‐channel bar inclined heterolithic stratification provides a unique sedimentological signature of multi‐channelled fluvial–tidal transitions that possess an open‐water lower basin with intrabasinal wind‐waves.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".